Sanitising URLs

package.json

@@ -29,7 +29,8 @@
     "deploy:site": "npx wrangler deploy"
   },
   "dependencies": {
-    "@modelcontextprotocol/sdk": "^1.11.0"
+    "@modelcontextprotocol/sdk": "^1.11.0",
+    "strict-url-sanitise": "^0.0.1"
   },
   "devDependencies": {
     "@axodotdev/oranda": "^0.6.5",

pnpm-lock.yaml

@@ -11,6 +11,9 @@ importers:
       '@modelcontextprotocol/sdk':
         specifier: ^1.11.0
         version: 1.11.0
+      strict-url-sanitise:
+        specifier: ^0.0.1
+        version: 0.0.1
     devDependencies:
       '@axodotdev/oranda':
         specifier: ^0.6.5
@@ -1346,6 +1349,9 @@ packages:
     resolution: {integrity: sha512-KXDYZ9dszj6bzvnEMRYvxgeTHU74QBFL54XKtP3nyMuJ81CFYtABZ3bAzL2EdFUaEwJOBOgENyFj3R7oTzDyyw==}
     engines: {node: '>=4', npm: '>=6'}
 
+  strict-url-sanitise@0.0.1:
+    resolution: {integrity: sha512-nuFtF539K8jZg3FjaWH/L8eocCR6gegz5RDOsaWxfdbF5Jqr2VXWxZayjTwUzsWJDC91k2EbnJXp6FuWW+Z4hg==}
+
   string-width@4.2.3:
     resolution: {integrity: sha512-wKyQRQpjJ0sIp62ErSZdGsjMJWsap5oRNihHhu6G7JVO/9jIB6UyevL+tXuOqrng8j/cxKTWyWUwvSTriiZz/g==}
     engines: {node: '>=8'}
@@ -2668,6 +2674,8 @@ snapshots:
 
   stoppable@1.1.0: {}
 
+  strict-url-sanitise@0.0.1: {}
+
   string-width@4.2.3:
     dependencies:
       emoji-regex: 8.0.0

src/auth/browser-provider.ts

@@ -1,6 +1,7 @@
 // browser-provider.ts
 import { OAuthClientInformation, OAuthMetadata, OAuthTokens, OAuthClientMetadata } from '@modelcontextprotocol/sdk/shared/auth.js'
 import { OAuthClientProvider } from '@modelcontextprotocol/sdk/client/auth.js'
+import { sanitizeUrl } from 'strict-url-sanitise'
 // Assuming StoredState is defined in ./types.js and includes fields for provider options
 import { StoredState } from './types.js' // Adjust path if necessary
 
@@ -29,15 +30,16 @@ export class BrowserOAuthClientProvider implements OAuthClientProvider {
     this.serverUrlHash = this.hashString(serverUrl)
     this.clientName = options.clientName || 'MCP Browser Client'
     this.clientUri = options.clientUri || (typeof window !== 'undefined' ? window.location.origin : '')
-    this.callbackUrl =
+    this.callbackUrl = sanitizeUrl(
       options.callbackUrl ||
-      (typeof window !== 'undefined' ? new URL('/oauth/callback', window.location.origin).toString() : '/oauth/callback')
+        (typeof window !== 'undefined' ? new URL('/oauth/callback', window.location.origin).toString() : '/oauth/callback'),
+    )
   }
 
   // --- SDK Interface Methods ---
 
   get redirectUrl(): string {
-    return this.callbackUrl
+    return sanitizeUrl(this.callbackUrl)
   }
 
   get clientMetadata(): OAuthClientMetadata {
@@ -143,13 +145,16 @@ export class BrowserOAuthClientProvider implements OAuthClientProvider {
     authorizationUrl.searchParams.set('state', state)
     const authUrlString = authorizationUrl.toString()
 
+    // Sanitize the authorization URL to prevent XSS attacks
+    const sanitizedAuthUrl = sanitizeUrl(authUrlString)
+
     // Persist the exact auth URL in case the popup fails and manual navigation is needed
-    localStorage.setItem(this.getKey('last_auth_url'), authUrlString)
+    localStorage.setItem(this.getKey('last_auth_url'), sanitizedAuthUrl)
 
     // Attempt to open the popup
     const popupFeatures = 'width=600,height=700,resizable=yes,scrollbars=yes,status=yes' // Make configurable if needed
     try {
-      const popup = window.open(authUrlString, `mcp_auth_${this.serverUrlHash}`, popupFeatures)
+      const popup = window.open(sanitizedAuthUrl, `mcp_auth_${this.serverUrlHash}`, popupFeatures)
 
       if (!popup || popup.closed || typeof popup.closed === 'undefined') {
         console.warn(
@@ -175,7 +180,8 @@ export class BrowserOAuthClientProvider implements OAuthClientProvider {
    * Retrieves the last URL passed to `redirectToAuthorization`. Useful for manual fallback.
    */
   getLastAttemptedAuthUrl(): string | null {
-    return localStorage.getItem(this.getKey('last_auth_url'))
+    const storedUrl = localStorage.getItem(this.getKey('last_auth_url'))
+    return storedUrl ? sanitizeUrl(storedUrl) : null
   }
 
   clearStorage(): number {

src/react/useMcp.ts

@@ -6,6 +6,7 @@ import { SSEClientTransport, SSEClientTransportOptions } from '@modelcontextprot
 import { StreamableHTTPClientTransport } from '@modelcontextprotocol/sdk/client/streamableHttp.js' // Added
 import { Client } from '@modelcontextprotocol/sdk/client/index.js'
 import { auth, UnauthorizedError, OAuthClientProvider } from '@modelcontextprotocol/sdk/client/auth.js'
+import { sanitizeUrl } from 'strict-url-sanitise'
 import { BrowserOAuthClientProvider } from '../auth/browser-provider.js' // Adjust path
 import { assert } from '../utils/assert.js' // Adjust path
 import type { UseMcpOptions, UseMcpResult } from './types.js' // Adjust path
@@ -23,7 +24,9 @@ export function useMcp(options: UseMcpOptions): UseMcpResult {
     url,
     clientName,
     clientUri,
-    callbackUrl = typeof window !== 'undefined' ? new URL('/oauth/callback', window.location.origin).toString() : '/oauth/callback',
+    callbackUrl = typeof window !== 'undefined'
+      ? sanitizeUrl(new URL('/oauth/callback', window.location.origin).toString())
+      : '/oauth/callback',
     storageKeyPrefix = 'mcp:auth',
     clientConfig = {},
     customHeaders = {},
@@ -189,7 +192,9 @@ export function useMcp(options: UseMcpOptions): UseMcpResult {
           authProvider: authProviderRef.current,
           requestInit: { headers: customHeaders },
         }
-        const targetUrl = new URL(url)
+        // Sanitize the URL to prevent XSS attacks from malicious server URLs
+        const sanitizedUrl = sanitizeUrl(url)
+        const targetUrl = new URL(sanitizedUrl)
 
         if (transportType === 'http') {
           transportInstance = new StreamableHTTPClientTransport(targetUrl, commonOptions)